1. Field of the Invention
The present invention relates to a rotational driving apparatus and to a manufacturing method therefor, for a disk recording medium, such as a floppy disk, in which a hub thereof is placed on a turntable and is centered.
2. Description of the Related Art
In a floppy disk, a metal hub is perforated with a center hole and a driving hole is disposed in the center of the disk as a flexible magnetic recording medium.
In a rotational driving apparatus for rotating the disk, a turntable is formed which includes a magnet for magnetically attracting the disk, a center axis projecting from a supporting surface of the turntable, and a driving pin projectably disposed from the supporting surface of the turntable supported by a plate spring or a swing arm.
When the disk is mounted, the center hole of the hub is inserted by the center axis of the turntable, and just after the turntable is started, the driving pin is inserted into the driving hole. Afterward, centering will take place to position the hub with respect to the turntable. In the centering, when the turntable is rotated, the center axis and the driving pin urge inner edges of the center hole and the driving hole of the hub, respectively, in directions opposing each other. At this time, the hub slides slightly on the supporting surface of the turntable.
In the state in which the hub is positioned on the turntable and is centered, as described above, the turntable, the hub, and also the combined disk and hub are rotated by a driving force of a motor driving unit applied to the turntable.
However, a rotor of the motor driving unit is not necessarily balanced by weight with regard to the rotational center, and the turntable is also imbalanced by weight with regard to the rotational center because the turntable has the driving pin and the supporting member. Therefore, nonuniform rotation is prone to be generated by the motor driving unit due to the imbalance of the rotating members including the turntable.
Conventionally, balance adjustment of the rotating members is performed when the motor driving unit is assembled or when the motor driving unit is assembled with the turntable and the driving pin.
However, a rotated member mounted on the turntable is not necessarily balanced with respect to weight. For example, the hub disposed in the center of the disk is perforated with a center hole so as to be inserted by the center axis of the turntable and the driving hole to be inserted by a driving pin. Both holes make the hub imbalanced with respect to weight around the center of the hub.
Accordingly, even if balance adjustment of the rotating members, including the motor driving unit or the turntable, is performed, as described above, the entire rotating portion will be weight imbalanced when a rotated member is mounted.
In a driving apparatus at a low rotational speed of approximately between 300 to 360 rpm, such as in conventional floppy disk driving apparatuses, the imbalance has little actual adverse effect on the rotation of the disk when only the balance adjustment of the motor driving unit or the turntable is performed.
In contrast, the driving apparatus for a high-bit-density floppy disk is very rapidly driven at a turntable rotation of several thousand rpm (for example, at 3600 rpm). Therefore, the imbalance provided by a rotated member mounted on the turntable has an effect on the rotation, such as vibration of the rotating portion, when the disk is driven, causing a probable adverse effect on servo movement of the motor.
Accordingly, to solve the above-mentioned problems in the conventional art, it is an object of the present invention to provide a rotational driving apparatus for a disk and a manufacturing method therefor (adjustment method) which prevent the rotation from vibrating and the like even if a rotated member mounted on the turntable is imbalanced.
A rotational driving apparatus for a disk according to the present invention comprises a turntable for magnetically attracting a hub disposed in the center of the disk, a center axis protruding at the rotational center of the turntable, a driving pin supported by the turntable so as to be projectable therefrom, and motor driving means for rotationally driving rotating members including the turntable, wherein rotational balance adjustment of the rotating members has been achieved by fixing, to the turntable, the hub having a center hole to be inserted thereinto by the center axis and a driving hole to be inserted thereinto by the driving pin, the hub attached to the disk, or a dummy member having the same distribution of weight as that of the hub.
A method for manufacturing (method for adjusting) a rotational driving apparatus for a disk according to the present invention comprises the steps of assembling a turntable for magnetically attracting a hub disposed in the center of the disk, a center axis protruding at the rotational center of the turntable, a driving pin supported by the turntable so as to be projectable therefrom, and motor driving means for rotationally driving rotating members including the turntable; and adjusting rotational balance of the rotating members by fixing, to the turntable, the hub having a center hole to be inserted thereinto by the center axis and a driving hole to be inserted thereinto by the driving pin, the hub attached to the disk, or a dummy member having the same distribution of weight as that of the hub.
In accordance with the present invention, in the state in which at least the hub or a dummy member having the same distribution of weight as that of the hub is fixed onto the turntable while the motor driving means and the turntable are assembled, the rotational weight balance of the entire rotating member is adjusted by partially adding or partially removing weight from the rotating members. Therefore, if the turntable is rotated in a state such that a rotated member formed of the disk and the hub is mounted thereon, the rotational balance cannot be disturbed. Furthermore, if the turntable is rotated at several thousand rpm, the vibration will not be generated.